[unreadable] Our overall goal is to develop new chemopreventive agents and regimens in animal models of estrogen receptor (ER) negative breast cancer, for eventual use to prevent this disease in women at risk. Our specific hypothesis is that the use of combinations of agents will be more practical and efficacious than use of single agents. However, many potentially useful chemopreventive agents have yet to be tested as single drugs for prevention of ER-negative breast cancer, so in a 5 year project, it will be necessary to evaluate these compounds first as single agents, before testing them in combinations. A second major hypothesis is that induction of apoptosis by non-cytotoxic chemopreventive agents in premalignant breast epithelium represents an important mechanism for prevention of ER-negative breast cancer. There are four Specific Aims in the project: Specific Aim 1: to establish a series of chemopreventive agents, to be used either singly or in combinations for prevention of ER-negative breast cancer; it is essential that these agents have known molecular targets. Specific Aim 2: to test the agents in Specific Aim 1 in selected mouse models of ER-negative breast cancer for their chemopreventive activity. Specific Aim 3: to identify useful markers and surrogate end-points, as well as classical histopathologic criteria, for evaluating the activities of agents shown to be useful in Specific Aim 2. Specific Aim 4: to evaluate the ability of the chemopreventive agents discussed in Specific Aim 1 to induce apoptosis in immortalized human breast epithelium, both non-neoplastic and neoplastic. We have assembled a series of preventive agents, including rexinoids, SERMs, vitamin D analogs, PPAR-gamma ligands, chromatin modifiers, and an EGF-receptor kinase inhibitor. These will be tested in several different transgenic and xenograft mouse models. We will establish a histopathologic scoring system for measuring severity of pre-malignant and malignant lesions, and will also use biochemical markers related to cell proliferation, cell differentiation, and invasiveness for evaluating effects of preventive agents. Finally, we will use standard techniques to measure apoptosis in breast epithelial cells in culture as well as in breast lesions in mice. These studies on apoptosis will be supplemented by measuring effects of chemopreventive agents on Myc gene expression. [unreadable] [unreadable] [unreadable]